1. Field of the Invention
The present invention is related to a lithography system.
2. Background Art
Pattern generators are used to form patterned radiation images in many environments. For example, pattern generators can be used in televisions, biomedical patterning applications, lithography, and the like.
When used in lithography systems, the pattern generators are used to pattern substrates during an exposure process. Example lithography systems include, but are not limited to, reflective or transmissive maskless, immersion, and mask-based photolithography. Example substrates include, but are not limited to, semiconductor wafers, flat panel display substrates, flexible substrates, and the like. Light interacting with an illumination spot on the pattern generator becomes patterned. The patterned light is projected using a projection optical system onto one or more target areas of the substrate during the exposure process to form features on the substrate.
Features larger than the projected image of the pattern generator are created by incrementing the substrate between exposure periods. However, any error in the distance the substrate is moved between exposures will lead to a finite region of either double exposure or no exposure on the substrate. To loosen the requirements on positioning of the substrate, a technique known as stitching may be used; the substrate is moved between exposures just less than the size of the projected image of the pattern generator yielding an overlap region. The spatial profile of the illumination of the pattern generator must therefore be modified such that the total intensity incident on the substrate in the overlap region from two exposures is equal to the total intensity incident on the substrate in the non-overlap regions. A trapezoidal illumination profile, as shown in FIG. 4, is one custom profile that accomplishes this.
The optimal location for the creation of a custom illumination profile that will not modify the pupil of the imaging system is at an image plane. The surface of the pattern generator is one such location. Therefore, what is needed is a system and method to modify the spatial response of a pattern generator.